dont really sure about linux but on windows -d1 only works in conjunction with -D1, as hashcat defaults to type2, so the right options for using cpu is
-D1 -d1
example plain cpu setup:
hashcat -d1 -b -m0
No devices found/left
hashcat -D1 -d1 -b -m0
Speed.#1.........: 1240.5 MH/s
-D1 -d1
example plain cpu setup:
hashcat -d1 -b -m0
No devices found/left
hashcat -D1 -d1 -b -m0
Speed.#1.........: 1240.5 MH/s